In recent years, the display elements of image display devices, such as television receivers, have been in a period of transition from the conventional cathode-ray tubes to thin display panels, such as liquid crystal panels and plasma display panels, enabling a decrease in the thickness of the image display device. A liquid crystal display device includes a liquid crystal panel that does not emit light by itself. Therefore, the liquid crystal display device requires a backlight unit as a separate lighting device. The backlight unit may be categorized into a direct type and an edge-light type in terms of their mechanism. In order to realize a further decrease in the thickness of the liquid crystal display device, an edge-light type backlight unit may be preferable, such as one described in Patent Document 1 indicated below. The example described in Patent Document 1 includes a light source disposed so as to face a light incident surface on one side surface of a light guide plate. On a back surface of the light guide plate, a reflection sheet with an extending portion is attached. The extending portion is folded toward the front side while enclosing the light source, with a folded distal portion adhesively affixed to a front side surface of the light guide plate through an adhesive layer.